Aquarius is one of the most ancient of constellations. The
Babylonians saw this area of sky as a man pouring water from a jar and it is
still represented this way today. Aquarius is one of the zodiacal
constellations and according to the Greeks it is linked to Ganymede, cup bearer
to the Olympic gods.
It’s in the Zodiac a belt of stars made up of 12
constellations that stretch around the sky, actually there are 13
constellations in the Zodiac, no one ever talks about Ophiuchus. The zodiac is
where the Sun, Moon and planets will always be found in the sky. Many people
get confused with astronomy and astrology, astronomy is the science of the
stars while astrology is the pseudo-science that tries to link people’s
characteristics with the positions of the planets against the starry
background.
The Arab astronomer Al Biruni saw it as Amphora a two
handled wine jar. The Egyptians referred to the constellation as Monius or
water. While in China with Capricorn, Pisces and a part of Sagittarius it was
seen as a serpent or turtle. The Anglo Saxons called it se Waeter-gyt the water
pourer.
Although Aquarius which can be seen in the autumn is the
10th largest constellation is not a particularly bright one. It can be found
below the square of Pegasus. The most prominent part of the constellation is
the Y shaped figure of 4 stars representing the water jar itself centred on the
star zeta. Together with gamma, eta and pi this little area is often called the
‘Water Jar’. With it being low in the sky any mist or moonlight means that not
even the brightest stars can be seen with the naked eye.
The brightest star is not alpha but beta whose name is
Sadalsuud which means ‘luck of lucks’ is of mag 2.8 and is about 540 light
years away. It is a G class supergiant with a temperature of 5,400`C slightly
cooler than the sun.
The second brightest star is alpha at mag 2.9 is
another G class supergiant star, again
slightly cooler than the Sun it has a
proper name which is sadalmelik which means ‘luck of the king’. Alpha is about
520 light years away. It has a surface temperature of around 4,900`C.
Delta or Skat which means ‘leg or shin’ is the third
brightest star at magnitude 3.3 and about 113 light years away. It is an A
class star with a surface temperature of about 8, 700`C much hotter than the
Sun.
The following stars make up the water jar
Gamma or Sadachbia, its name means ‘luck of the homes’
(tents).The star has a magnitude of 3.8
and is 164 light years distant. It is an A class star with a surface
temperature of about 10,200`C, our Sun is about 5,800’C
Zeta which is slightly above and to the left of gamma is an
unnamed and is a binary star, which
means there are two stars here, however without a small telescope you would not
be able to see the two stars. Zeta is located at the centre of the water jar
asterism. The two stars are yellow white type stars one is a F3 star at
magnitude 4.2 the other a F6 giant at magnitude 4.5 . Both are hotter than the
Sun . The pair are 92 light years away and when we put the brightness of the
two stars together they appear in the sky as a single star to the naked eye as
a star of magnitude 3.6.
To the left of zeta is eta is a star of magnitude 4.0 and is
168 light years away, It is a B class star with a surface temperature of 11,000
degrees ‘ C twice the temperature of the Sun.
Just to the right of zeta is pi the faintest of the water
jar group of stars at magnitude 4.6, it is a B class giant star with a whopping large temperature
of 26,700’ C. Pi is 780 light years away.
One other star I feel I need to mention is :-
TRAPPIST -1 which stands for Transiting Planets and
Planetesimals Small Telescope. A solar system with 7 Earth size planets. They
all are between the size of Mars and Earth. The system lies around 40 light
years away. It is too faint to be seen
with the naked eye.
As the title of the project indicates astronomer are
searching for planets transiting or passing in front of the star they orbit.
TRAPPIST -1 was discovered back in 2016.
The star in question here is a small red dwarf star. It is
much smaller than our Sun. Astronomers want to know if any of the planets can
support life. One big problem with red dwarf stars is that they produce very
powerful flares which may make it very difficult if not impossible for life to
exist on any plants orbiting a red dwarf star.
The idea of looking for a slight change in brightness of a
star when something passes in front of it is not new. The idea was first put
forward by the deaf astronomer John Goodricke in York in 1782. Collaborating
with his colleague Edward Pigott together they observed a star in the
constellation of Perseus. The star called ALGOL t marks the eye of the medusa.
The star names are Arabic and Algol means the ‘Winking Demon’. We know today
that Algol is a double star system and the stars are orbiting and eclipsing
each other causing the brightness of the star to change. With the star names
being Arabic I wonder if the Arab astronomers also realised that this star
changed in brightness. If they did no records have survived. The light changes
on Algol are much more than on TRAPPIST-1.
In the 18th century the French astronomer was
looking for comets. He found around a dozen or so, non were particularly
import, however he kept coming across a large number of fuzzy looking objects
similar to comets. These caused him a lot of problems so he drew up a list on
non-comet objects to avoid becoming confused with these objects. It is strange
to report today that his comets are nearly forgotten to history but that his
list of non-comet objects The Messier List of 110 objects is still used by
astronomers today.
There are two Messier objects: -
Messier 2
A globular cluster discovered by the Italian astronomer
Maraldi on September 11th 1746, who believed it to be a nebulous star. Globular clusters are densely packed
collections of ancient stars. Roughly spherical in shape, they contain hundreds
of thousands, and sometimes millions of stars.
Charles Messier rediscovered the cluster exactly 14 years
later on September 11th 1760. It was only in 1783 that William Herschel who 2
years earlier had discovered the planet Uranus was able to see through a larger
telescope and realise that M2 was made up of numerous stars.
M2 has a diameter of about 175 light years and contains
about 150,000 stars, it is one of the most compact globular clusters, and most
of the brightest stars are red and yellow giant stars. M2 appears to be about
13 billion years old that is about 3 times the age of the Earth and Sun. M2 is
about 33,000 light years away.
M2 is north of Beta
Aquarii, M2 has a magnitude of 6.5 which
means that it is below naked eye
visibility but can easily been seen with a pair of binoculars. In binoculars it
will appear as a large, fuzzy ball with little or no resolution. It is possible
to just see some stars around the edge using a 6 inch telescope, a larger
telescope above 10 inch will resolve into stars.
In the 1830s, John Herschel (son of William who discovered
the planet Uranus in 1781) saw it as “It
is like a heap of fine sand!” which is perhaps as apt a description as can be
rendered. Through a large telescope, the globular cluster does resemble a
glittering mass of sparkling granules.
Messier 72
M72 is east of the 3.8 mag star epsilon Aquarius, this is
the faintest globular cluster in the Messier list.
At mag 9.2 this globular is easy to miss, M72 actually
spreads across 98 light years and like M71 is classified as a good open
globular, and is 56,400 light years away.
It can just be glimpsed in larger binoculars but require a
reasonable size telescope to see it well. The cluster is racing towards us at
about 160 miles per second so maybe many 1000s of years from now owners of
small telescopes will be able to see it better.
Messier first observed M72 in 1780 who said its light was
faint
M73
This was one that fooled Messier in that it is not a star
cluster of galaxy but just a close group of stars. A trio of 10th mag stars in
a poor field is in Aquarius is how Admiral Smyth described this most
unremarkable Messier object in his Cycle of Celestial Objects published in the 19th century .
This group of stars is situated close to M72 and is
actually a grouping of 4 stars with no apparent connection, except that they
lie in the same line of sight. Asterisms like this can be seen in any part of
the sky. Messier just got fooled by it.
The optics of Messier’s telescope were not as good as modern
optics and this is why the group probably looked fuzzy to him. This could have been combined with poor
atmospheric conditions when he observed them.
Messier first observed M73 in 1780 and described it as a
cluster of 3 or 4 faint stars which at first glance resembles a nebula, and
which does contain some nebulosity.
Although the stars appear to be close together in space in
fact they are not. The stars are all at different distances to the Earth. The
stars appear as an object of magnitude 9. They cannot be seen with the naked
eye and a reasonably large telescope would b needed to see them.
There are two other nebulous objects to mention on Aquarius
, the first is NGC 7009 the Saturn Nebula so named because it looks the planet
Saturn. The letters NGC stand for the New General Catalogue that was introduced
in 1888, even today we still use the term NGC. It is a planetary nebula this is a star in the
process of throwing all of its gas away into space before it becomes a white
dwarf star. This is the ultimate fate for our Sun in a few billion years’ time.
It was discovered by William Herschel in 1783 he thought it
looked a little like a planet hence the name planetary nebula. This nebula is
around 5,200 light years away.
The name Saturn
nebula was given to the object by Lord Rosse from his observatory at Bir Castle
in Ireland using what at the time was the largest telescope in the world. The
telescope had a mirror 72 inches wide was built in 1845.
Here is another planetary nebula in Aquarius this is NGC
7293 the Helix Nebula which at 655 light years distance is the closest
planetary nebula to us.
Meteor showers
There are two meteor showers associated with Aquarius.
Meteors or shooting stars as many people like to call them are connected to
comets. They have nothing at all to do with stars but are grains of dust that
burn up as they enter the Earth’s atmosphere. A comet is a large dirty snowball
travelling around the Sun, it leaves a trail of dust behind it and if the Earth
happens to pass through one of these dust streams we see lots of meteors or a
meteor shower. There are several meteor showers during the year.
The eta Aquarids meteor shower occurs during early May with
the maximum number of meteors seen around the 5th May when around 40 meteors per hour can
be seen. The meteor shower is so named because all the meteor in the sky seem
to start their path across the sky from the star eta Aquarius. The comet
connected with this meteor stream is none other than Halley’s Comet. There are
two meteor showers connected with Halley’s comet, the other is in October and
is called the Orionids.
The second meter shower is the delta Aquarids which peaks
around abut July 30th when around 20 meteors per hour can be seen.
This meteor shower is connected with comet Macholtz .
www.theramblingastronomer.co.uk
